Fire on n islands
Source: 2023 Singapore MO Round 2 Senior Q3
June 24, 2023
combinatorics
Problem Statement
Let be a positive integer. There are islands with bridges connecting them such that one can travel from any island to another. One afternoon, a fire breaks out in one of the islands. Every morning, it spreads to all neighbouring islands. (Two islands are neighbours if they are connected by a bridge.) To control the spread, one bridge is destroyed every night until the fire has nowhere to spread the next day. Let be the minimum possible number of bridges one has to destroy before the fire stops spreading. Find the maximum possible value of over all possible configurations of bridges and island where the fire starts at.